1. Field of the Invention
The present invention relates to a novel metallic oxide and to a process for manufacturing such a metallic oxide, and more particularly, to a boron-containing metallic oxide and to a process for manufacturing such a metallic oxide. Also, the invention can be used in a superconducting material and is also applicable to various fields, such as sensors, electronic devices, computers, medical instruments, magnets, transmission lines, energy equipment, voltage standard, and the like. Further, the metallic oxide of the present invention is particularly effective in the form of a wire and a thick film and is also applicable when it is bonded with or dispersed in other oxides or metals.
2. Description of the Related Art
Copper-containing metallic oxide superconducting materials have been discovered one after another in recent years. Such materials have much higher superconducting critical temperatures (Tc) than those of conventionally-known niobium-type materials. Because of this advantage, various research has been made to apply such materials in many fields.
Among these copper-containing metallic oxide superconducting materials, the following types are particularly known: YBa.sub.2 Cu.sub.3 O.sub.y referred to as the Y type, Bi.sub.2 Sr.sub.2 Ca.sub.n Cu.sub.1+n O.sub.y (n=0,1,2,) referred to as the Bi type, Tl.sub.2 Ba.sub.2 Ca.sub.n Cu.sub.1+n O.sub.y (n=0,1,2) referred to as the Tl type, and the like. Research is currently in progress to put these types of materials to practical use.
Also, in particular, as a boron (B)-containing metallic oxide superconducting material, Physica C, Vol.205 (1993) , p.118-122 introduces a material having a composition of YSr.sub.0.8 Ba.sub.1.2 Cu.sub.2.5 B.sub.0.5 O.sub.7 and a superconducting critical temperature Tc of 51K.
Among the above-noted metallic oxide superconducting materials, the Y-type and Tl-type materials present the following problem when applied to superconducting wires or magnetic shield thick films. The crystal grains in the grain boundary tend to bond weakly with each other, that is, they suffer from, what is called, "a weak link", thereby resulting in a failure to increase the critical current density. Such a conventional problem is disclosed in SCIENCE Vol.259 (1993) p.306-308 and INDUSTRIAL MATERIAL Vol.41 (1993.3) p.18-25, and the like.
Further, among the foregoing metallic oxide superconducting materials, when the Bi type is applied to a wire or a thick film, unlike the Y type and Tl type, the crystal grains in the grain boundary are unlikely to suffer from a weak link, thus exerting outstanding two-dimensional crystalline characteristics, thereby enhancing the easy application of the Bi type to a wire. On the other hand, however, the Bi type has a problem in that the critical current density significantly decreases in the magnetic field. This symptom becomes particularly noticeable at a magnetic field of 1 tesla or more and at a temperature of 30K or more, thus significantly hampering applications of the Bi type to important fields, for example, to a superconducting magnet. Such a conventional problem peculiar to the Bi type is also disclosed in detail in SCIENCE Vol.259 (1993) p.306-308 and INDUSTRIAL MATERIAL Vol. 41 (1993.3) p. 18-25 and p. 26-31, and the like.
Taking such current conditions into consideration, it is confirmed that for application to a magnet, or the like, it is important to develop a Y-type material which will not be likely to suffer from a weak link.